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DTC codes / U01xx · Lost communication with a control module / U0105

U0105Lost Communication With Fuel Injector Control Module

U0105 indicates that the engine control module (ECM) or another primary controller has lost communication with the fuel injector control module (FICM) over the controller area network (CAN) bus. The ECM expects regular status messages from the FICM and sets this code when those messages stop arriving within the required time window, pointing to a wiring, power, or module fault rather than a direct injector failure.

SystemNetwork
Code typeGeneric (all makes)
SeverityHigh
Fix difficultyProfessional
AreaLost communication with a control module

Symptoms you may notice

  • Illumination of the check engine light or service engine soon light, often with no other noticeable symptoms.
  • Engine cranks but fails to start or starts and immediately stalls because injector pulses are not being delivered.
  • Rough running, misfiring, or a significant loss of power while driving.
  • Reduced fuel economy or a rich-running condition if the FICM defaults to a limp mode.
  • Other communication-related codes stored in multiple modules, indicating a bus-wide issue.
  • Intermittent stalling or a no-start that comes and goes with temperature or vibration.

Common causes, most likely first

  1. Damaged, corroded, or disconnected wiring in the CAN bus circuit between the ECM and FICM.
  2. Blown fuse or faulty relay in the FICM power supply circuit.
  3. Poor ground connection at the FICM mounting point or engine block.
  4. Failed fuel injector control module due to internal electronics failure.
  5. Water intrusion or connector corrosion at the FICM harness, common on vehicles with underhood module placement.
  6. A shorted or open CAN bus wire elsewhere in the network that disrupts communication for multiple modules.
  7. Low battery voltage or a failing charging system that causes modules to drop offline intermittently.

How to diagnose and fix it

  1. Perform a visual inspection of the FICM connectors and harness for corrosion, chafing, or loose pins, and check all related fuses and relays.
  2. Measure battery voltage and charging system output to rule out low-voltage communication dropouts.
  3. Use a scan tool to check for communication with the FICM directly; if it cannot be addressed, proceed to circuit testing.
  4. Disconnect the battery and use a multimeter to check continuity and resistance on the CAN bus wires between the ECM and FICM, looking for opens or shorts.
  5. Check power and ground at the FICM connector with the key on, verifying that the module receives the correct voltage and has a clean ground.
  6. If wiring and power are good, substitute a known-good FICM or perform a module swap to confirm the fault before replacement.
  7. After repair, clear codes and verify that communication is restored and no related codes return during a road test.

What most technicians overlook on U0105

  • A failed FICM often sets U0105 alongside injector circuit codes, so technicians who replace injectors first waste money when the module itself is the root cause.
  • Corroded ground straps on the engine block can cause intermittent FICM communication loss that only appears under load or after the engine warms up.
  • The CAN bus is a shared network, so a shorted wire in an unrelated module can pull down the entire bus and set U0105 even though the FICM is healthy.
  • Some vehicles require a relearn or programming procedure after FICM replacement, and skipping it can leave the code stored even with a new module.
  • Battery voltage that drops below 10 volts during cranking can cause the FICM to reset and set U0105 without any permanent wiring fault.

Can I keep driving with U0105?

Do not continue driving with U0105 because the engine may stall without warning or fail to restart, creating a safety risk. Have the vehicle towed to a repair facility if it is not running, or limit driving to a short distance to a safe location if it is still mobile.

Tools that help

Tools we recommend are in the Auto Veteran shop on Amazon. As an Amazon Associate we earn from qualifying purchases.

Guidance is general and written for all OBD-II vehicles. Exact tests and values vary by model, so confirm the fault before replacing parts.

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